sorry if this questions has been asked a millions times, i searched and couldnt find anything. any ways when it comes to cars i like to think i know enough to get around. i got into a debate with my friend about cars exploding in a car accident. that they just catch fire, and the news and other people blow the story out of porportion. any how this is my theory on why they cant explode unless with c4 or dynamite.
1.) not enough atmospherice pressure
2.) the only time air is let into the car is in the CyClinder with the air fuel mixture.
3.) there is no air in the gas tank and if a leak let in air in the gas tank it would just leak out.
4.) you never see cars in crash test, nascar, crash car derbys, or any other motorsport Blow up but just catch fire.

his only defense was he saw a car blow up and blaha, blah,blah. whch i think where just sparks.

if anybody could give more information to inlighten me on this subject please do.

Engines can, and do, explode. But not with Hollywood intensity. Batteries can explode, as well; but that won't take out the whole car.

A collision resulting in a fire could conceivably result in a gas tank exploding, if the fire was allowed to burn. A ruptured gas tank can yield quite a fire, but if it's ruptured there won't be an exxplosion.

but if there is no Air in the gas tank, how does the car explode, it seems to me that the gas would just burn. gas is pulled out of the gas tank by a fuel filter inside or outside sometimes both the gas tank is also in the back of the car then the engine is in the front where the air fuel mixture is mixed from the carb/fuel injection, and then blown up in side the cyclinder with the up motion of the pistons to the spark plug. my questions is more directed towards gas tanks.

Any time that there's a fair quantity of gasoline around, explosion is a possibility. The likelihood of a car exploding is rather low, probably about one ten-thousandth of what you see in the movies, but it's still not zero.

I read somewhere that the vapor pressure of gasoline is so high that normally a gas tank won't ignite because the fumes are too rich to ignite (whereas in a diesel tank the fumes are too lean). Of course, if the tank ruptures that would change.

I'm trying to find a cite for this but can't remember where I read it.

Batteries, tires, front and rear bumpers, air bags, lift gate mechanisms and ferocious gas fed fire, but no explosions, in about 1000 car fires over a 35 year career of firefighting. But that's not to say that I didn't expect one every time one was out of control. And you will wet your pants when a tire blows.

I've seen a car explode, but not as a result of a collision. My coworkers and I noticed smoke appearing outside the windows of our office building one morning and looked out to discover a woman in a lot of distress standing next to her truck in a parking lot across the street. She had apparently noticed smoke coming into the vehicle, pulled over into the parking lot, and popped the hood to discover the engine was in flames. We called the fire department right away of course, but there were several minor explosions and then a big WHOOM and fireball which engulfed the car before the firefighters arrived there. It burned very quickly.

I've seen cars explode on TV. Not movie fo the week TV but science show TV. Specifically they were testing something to help limit gas tank explosions. Essentially the put a steel mesh inside of the gas tank. The mesh was fairly dense and filled the gas tank completely but they showed it barely lowered the gas tanks fuel capacity. After that they intentionally set fire to two cars in sucha fashion as to ensure a gas tank explosion. The car with the mesh had an explosion but it was 'minor' compared to the car without the mesh.

That said the explosion in the car without the mesh was nowhere near what you usually see in movies*. A big *FOOMP* that popped the back end up a bit and set the interior of the car on fire. I doubt the explosion would have killed a driver by itself (although with the interior now on fire the driver had better be vacating the car pronto).

I have seen a few car fires in real life (not involved in them) and have yet to see one explode. Anecdotal and admittedly limited in number but there for what it is worth.

*Another movie gimmick that generally doesn't reflect real life is what guns sound like when fired. They are much more impressive in the movies compared to the more firecracker like sound in real life (of course depending on the gun you are using...some are nothing like firecrackers). I lived in a neighborhood in Chicago for awhile where it wasn't uncommon to here a gunshot at least once a week. I initially thought they were firecrackers till a cop I happened to be talking to one day told me differently. Another friend of mine who is also a police officer confirmed it (I specifically asked him in case the first officer was pulling my leg). He said you could sort of guess at what you were hearing by counting how many cracks you heard. People rarely set of three firecrackers in short succession and leave it at that.

Originally posted by Gary T And there is always air in the gas tank. The lower the fuel level, the more air.

Air is a bit of a misnomer here. There is gas vapor inside the tank. The vapor being heavier than air displaces the oxygen and nitrogen so you are left with liquid gas and gas vapor. This is why in tank fuel pumps have sparks at the armature, but there is no fire due to the lack of oxygen.
So can a car explode?
Sure they can, but the odds of it happening is real rare. In the event of a fire any undeployed airbag is more likely to detonate than a gas tank. To get a fuel tank explosion would require a punctured tank, a gas spill and and ingition source. That would give you an explosion, not just a fire.

Originally posted by Rick Air is a bit of a misnomer here. There is gas vapor inside the tank. The vapor being heavier than air displaces the oxygen and nitrogen so you are left with liquid gas and gas vapor. This is why in tank fuel pumps have sparks at the armature, but there is no fire due to the lack of oxygen.
So can a car explode?
Sure they can, but the odds of it happening is real rare. In the event of a fire any undeployed airbag is more likely to detonate than a gas tank. To get a fuel tank explosion would require a punctured tank, a gas spill and and ingition source. That would give you an explosion, not just a fire.

no that wouldnt give it an explosion either. we just tested with a car from teh scrap yard, we filled up the gas tank closed the cap started a fire the inside of the fuel line, waited 5 minutes the inside of the car was inflames another 5 minutes later the whole car was inflames. we waited 30 more minutes for an explosions. no explosion came. also note all gas was burnt up inside the tank,and much to my surprise all fuel lines where still good except the fuel filtes inside and out and the floater gas level and tubing inside the tank. next test was to fill up the tank again with 91 octane hook a water hose up too the inside of tank(like in the movies) sill it with a towel we then syhpened some gas out and lighted the spilled gas on fire, no explosion happened same thing has before but started from the out side and worked it's way in. next test was to shoot the gas tank with a shot gun then ignite the rupture tank(like in the movies again). No explosion occurred. but gas spallter on the exit side of the bullet so we had more fire then ecepted when we ignited the spilled gas. so like all people said it is really rare, and damn near impossible to explode i dont know what these findings mean since also it was only one car and not hunderds.

As a point of information, I once watched the proceedings after a joy-rider slammed a car at high speed into a wall. He crawled out with some knocks but in reasonable shape, threw what I can best describe as a lit petrol bomb onto the front seat, and quickly disappeared in the opposite direction to the approaching sirens.

There was a brief "woof" when the petrol bomb blew, and a pretty strong fire spread fairly quickly. It then burned for maybe 20-30 minutes, gradually spreading throughout the car. The fire guys arrived, but said they weren't going near it..it was already a write-off and there was no point.. Eventually it spread to the rear, and got the fuel tank..there was another "woof", nothing very dramatic, and the fire flared brighter for a few minutes. Then the fire guys went over and doused the whole thing in foam, totally extingushing the fire in about 60 seconds. So even when the fuel tank went, it wasn't what I would call an explosion. Obviously I don't know how full the tank was.

A VW microbus exploded while I was driving it. Big KABOOM, rear end of vechicle lifted off the ground a little, then a small fire in the engine compartment that I put out with roadside gravel. It was the engine's oil pan that blew, not the gas tank. I expect that somehow gas made it into the oil pan, altough I don't know how.

__________________
Hour after hour, day after day, we paddled and sang and slept under the hot sun on the northern ocean, wanting never to return.

My favorite TV car explosion was in a Nash Bridges episode where a car had crashed into a condo and was then shot with some stray bullets and the gas tank began leaking, and the electrical wiring above began sparking with the bad guy's leg trapped in the windshield. So Nash and his partner see the gas drip and the ceiling electrical spark, which in this case is not throwing off any significant spark debris, and is at least 14 -20 feet away from the gas puddle and dive out the window. A microsecond later an explosion ensues that literally blows the entire multi-condo section to bits and looks like the condos were it with a daisy cutter bumb dropped from a B52.

Originally posted by Rick Air is a bit of a misnomer here. There is gas vapor inside the tank. The vapor being heavier than air displaces the oxygen and nitrogen so you are left with liquid gas and gas vapor. This is why in tank fuel pumps have sparks at the armature, but there is no fire due to the lack of oxygen.
So can a car explode?
Sure they can, but the odds of it happening is real rare. In the event of a fire any undeployed airbag is more likely to detonate than a gas tank. To get a fuel tank explosion would require a punctured tank, a gas spill and and ingition source. That would give you an explosion, not just a fire.

Air must be allowed in as fuel is removed, otherwise the fuel pump will not work as it should. This air gets saturated with gasoline vapour to the point of the vapour pressure of the gasoline remaining in the tank.

It's possible we are saying the same thing, but I am not certain from your post.

[nitpick] Vehicles themselves, as a whole, will not explode. As ltfire correctly pointed out, there are many things ON the vehicle that will explode such as tires (by far the worst, and damn scary when you're ass-deep in an engine compartment trying to get a knock on the burning car) air bags, lift mechs, and even refrigerant storage units, (which, a while back we were notified were being filled with propane by shde tree mechanics to save a bit of money) but the cars themselves...nope [/nitpick]

All that having been said, Whilst in my various and sundry fire investigation classes over the years, I've actually used explosives to detonate a car, and to precisely flip the thing over from front to back to make it land on its' roof. Pretty cool, except the car never explodes in a fireball the way it does in the movies, for that, you need low order explosives and half full gas cans, which the instructor in one of my classes did, and it was completely hollywood, and completely unrealistic.

Try as you might, there is nothing that will encourage a car to explode. Another misnomer on a slightly different subject...

When you have a fire in, say, a bedroom of your house, it is not, per se a structure fire, it is called a room/contents fire, when it breaches the protective skin of the dryboard and begins to burn the structural members of the house, THEN it is a structure fire.

Originally posted by Anthracite Air must be allowed in as fuel is removed, otherwise the fuel pump will not work as it should. This air gets saturated with gasoline vapour to the point of the vapour pressure of the gasoline remaining in the tank.

It's possible we are saying the same thing, but I am not certain from your post.

the fuel pump on the outside of the gas tank on the fuel line is Mechanical so no air is needed. it sucks it out while the other fuel pump in side the tank pushes out the fuel again both are mechanical.

Originally posted by johnnydigital the fuel pump on the outside of the gas tank on the fuel line is Mechanical so no air is needed. it sucks it out while the other fuel pump in side the tank pushes out the fuel again both are mechanical.

It doesn't matter what type of fuel pump is used, or where it's located. If gas is going to be moved out of the tank, something has to take its place--otherwise, a vacuum will form and the gas will stop leaving the tank despite the fuel pump's efforts. This is basic physics--you can't pour (or pump) liquid out of a container if nothing can get in to fill the space once occupied by the liquid. The something that takes the place of the departing gas is air.

Gasoline has a very narrow flammable range of about 0.8 to 6% gasoline vapor in air. In other words, the vapor-air mixture must be exactly as specified or the gas
will not burn, let alone explode! Note that we say vapor. Liquid gasoline must change into vapor before it can burn (although this is no huge problem since it easily
vaporizes).

For a car to explode during impact the tank must catastrophically rupture and spew a fine mist of gasoline over a large area so it can vaporize and mix with air in
exactly the right proportions. The mixture must then find a source of ignition. Automobile gas tanks are built to withstand a considerable impact force and are
usually located in a protected area between the beams of a car's frame. Common ignition sources in the car's engine are generally at the other end of the vehicle.

Originally posted by frithrah Liquid gasoline must change into vapor before it can burn (although this is no huge problem since it easily
vaporizes).

True enough. I saw a guy snuff a lit cigarette in a cup of gasoline. He was intentionally doing this to show just what you said but I think it is a stupid thing to try in general (so in other words don't try this at home kids). It is quite possible for gas to have evaporated at the surface and that could ignite as the cigarette goes for the liquid gas beneath.

Caught a 5 gal can of gas on fire once. As the plastic can melted, the gas ran out and increased the fire many fold. I just kept sweeping it away for the building with the garden hose and let it burn while hopping that it would keep burning and not allow to much vapor to get away in an unburned state.

The firestorm looking tornado climbing up about 50 feet was a much harder thing to control and scorched the building a bit.

To keep the fire away from the building I needed to be between the building and the fire and that was only about 10 feet so I got a bit warm.

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